Schematic picture of the phylogenetic relationship and the functional domains within the Adhesion GPCR family in amphioxus and human. The tree is based on a neighbor-joining tree bootstrapped 500 times. The colours of the leaves denote the species; orange for amphioxus and purple for human genes. The leaves also show the domains of the N-termini, except in two explicitly marked cases were it is C-termini that contain the domains. The domain search in amphioxus was made with the HMMER package, an e-value cut-off at 0.01 and the local PFAM models. Human domains were adopted, along with group annotations, from [13]. The symbols and abbreviations are shown in the lower left corner. The abbreviations stand for: GPS, GPCR proteolytic site; EGF, epidermal growth factor; HBD, hormone-binding domain; Ig, immunoglobulin; OLF, olfactomedin; GBL, galactose-binding lectin domain; CA, cadherin domains; LamG, laminin; LRR, leucine rich repeats; SEA, sperm protein, enterokinase, and agrin; TSP, thrombospondin; PTX, pentraxin domain. In the upper left corner are the domains unique for amphioxus. The abbreviations are: LDLa, Low-density lipoprotein receptor domain class A; SMB, Somatomedin B domain; DS, discoidin; I-set, Immunoglobulin I-set domain; CUB, CUB domain; LectinC, Lectin C-type domain; TNFR, TNFR/NGFR cysteine-rich region; Kringle, Kringle domain; SRCR, Scavenger receptor cysteine-rich domain.

The figure summarizes our findings in amphioxus in comparison with human GPCRs. The shape of the tree and the division are adopted from [4] and the black dots represent core nodes. The families are GLU, Glutamate; Rhod, Rhodopsin; ADH, Adhesion; FZD/TAS2, Frizzled/Taste2; SEC, Secretin; OA, Ocular albinism receptors; VR, Vomeronasal receptors. The Rhodopsin family is further split into α-, β- γ- and δ-groups. The subgroups in α are AMIN, serotonin/dopamine/adrenergic/trace amine receptors; MEC, melanocortin/Lysophospholipid (EDG)/adenosin/cannabinoid receptors; MTN, Melanotonin receptors; OPN, opsin-like receptors; PTG, prostaglandin receptors. In γ: CHEM, Chemokine-like receptors; MCH, Melanocyte concentrating hormone receptors; SOG, somatostatin/opioid/galanin receptors. In δ: LGR, glycoprotein binding receptors; MRG, MAS-related receptors; OLF, olfactory receptors; PUR, purine-like receptors. Orange leafs only hold amphioxus transcripts, purple only human and green leaves represent branches that hold genes from both species. The annotation at the end of each leaf is the number of GPCRs in each branch. The number without parenthesis is for amphioxus and that one within parenthesis is the number of human GPCRs according to [13].

Distribution of the number of different GPCR families in A) amphioxus, B) Humans and C) All animals, displayed on a logarithmic scale. The Animal diagram is based on an average for amphioxus, humans, Mus musculus, Gallus gallus, Danio rerio, Takifugu rubripes, Ciona intestinalis, Drosophila melanogaster, Anopheles gambiae and Caenorhabditis elegans. The numbers for humans and M. musculus are from [13], G. gallus from [8] and for the remaining species from [4].